Polycrystalline diamond element

ABSTRACT

A PCD insert comprises a PCD element joined to a cemented carbide substrate at an interface. The PCD element has internal diamond surfaces defining interstices between them. The PCD element comprises a masked or passivated region and an unmasked or unpassivated region, the unmasked or unpassivated region defining a boundary with the substrate, the boundary being the interface. At least some of the internal diamond surfaces of the masked or passivated region contact a mask or passivation medium, and some or all of the interstices of the masked or passivated region and of the unmasked or unpassivated region are at least partially filled with an infiltrant material.

FIELD

This invention relates to polycrystalline diamond (PCD) elements, bodiesand tool inserts, particularly for use in tools for boring into theearth, and to a method for making PCD elements.

BACKGROUND

Cutter inserts for drill bits for use in boring into the earth maycomprise a layer of polycrystalline diamond (PCD) bonded to a cementedcarbide substrate. Such cutter inserts may be referred to aspolycrystalline diamond compacts (PDC).

PCD is an example of a superhard, also called superabrasive, materialcomprising a mass of substantially inter-grown diamond grains, forming askeletal mass defining interstices between the diamond grains. PCDmaterial comprises at least about 80 volume % of diamond and may be madeby subjecting an aggregated mass of diamond grains to an ultra-highpressure of greater than about 5 GPa and temperature of at least about1,200 degrees centigrade in the presence of a sintering aid.

Suitable sintering aids for PCD may also be referred to as a catalystmaterial for diamond. Catalyst material for diamond is understood to bematerial that is capable of promoting direct inter-growth of diamondgrains at a pressure and temperature condition at which diamond isthermodynamically more stable than graphite. Some catalyst materials fordiamond may promote the conversion of diamond to graphite at ambientpressure, particularly at elevated temperatures. Examples of catalystmaterials for diamond are cobalt, iron, nickel and certain alloysincluding any of these. PCD may be formed on a cobalt-cemented tungstencarbide substrate, which may provide a source of cobalt catalystmaterial for the PCD. The interstices with PCD may be at least partly befilled with a material, which may be referred to as a binder or a fillermaterial. In particular the interstices may be wholly or partiallyfilled with catalyst material for diamond.

Components comprising PCD are used in a wide variety of tools forcutting, machining, drilling or degrading hard or abrasive materialssuch as rock, metal, ceramics, composites and wood-containing materials.For example, PCD bodies are commonly used as cutter inserts on drillbits used for boring into the earth in the oil and gas drillingindustry. PCD bodies are also used for machining and millingmetal-containing bodies, such as may be used in the auto manufacturingindustry. In many of these applications the temperature of the PCDmaterial becomes elevated as it engages a rock formation, workpiece orbody with high energy.

PCD is extremely hard and abrasion resistant, which is the reason it isthe preferred tool material in some of the most extreme machining anddrilling conditions, and where high productivity is required. Adisadvantage of PCD containing certain catalyst materials for diamond asa filler material may be its relatively poor thermal stability aboveabout 400 degrees centigrade. The catalyst material may promote thedegradation of the PCD at elevated temperature, particularly attemperatures greater than about 750 degrees centigrade, as may beexperienced in manufacture and use of PCD compacts.

U.S. Pat. No. 7,377,341 discloses thermally stable ultra-hard compactconstructions comprising a body formed from an ultra-hard material suchas PCD, including a thermally stable region positioned adjacent aworking surface of the body. The ultra-hard material body can beattached to a desired substrate, thereby forming a compact, and anintermediate material can be interposed between the substrate and thebody. The intermediate material may be one that does not infiltrate intothe ultra-hard material body during high pressure/high temperatureprocessing and that can operate as a barrier to prevent migration ofconstituent materials from the substrate to the ultra-hard materialbody.

U.S. Pat. No. 7,473,287 discloses thermally-stable polycrystallinediamond materials comprising a first material phase that includes aplurality of bonded together diamond crystals, and a second materialphase that includes a reaction product formed between a binder/catalystmaterial used to facilitate diamond crystal bonding and a material thatis reactive with the binder/catalyst material. A barrier layer may beplaced between PCD material and a substrate to prevent unwantedinfiltration of extra cobalt therein which could adversely impact thethermal stability of the resultant PCD material.

United States patent application publication number 2007/0079994discloses thermally stable diamond-bonded compacts that include adiamond-bonded body comprising a thermally stable region that extends adistance below a diamond-bonded body surface. The thermally stableregion has a material microstructure comprising a matrix first phase ofbonded together diamond crystals, and a second phase interposed withinthe matrix first phase. The second phase comprises one or more reactionproducts formed between one or more infiltrant material and the diamondcrystals at high pressure/high temperature (HPHT) conditions. Theinfiltrant or replacement material may include one or more of thefollowing elements: Si, Cu, Sn, Zn, Ag, Au, Ti, Cd, Al, Mg, Ga, Ge,which may also be used in compounds containing conventionalsolvent-catalyst materials (transition metals) where the solventcatalyst is rendered inactive by reaction with another material.

United States patent application publication number 2008/0115421discloses a method of fabricating a superabrasive article, in which atleast a portion of interstitial regions of apre-sintered-polycrystalline-diamond body may be infiltrated withsilicon from a silicon-containing material. At least a portion ofmetal-solvent catalyst located within the at least a portion ofinterstitial regions of the pre-sintered-polycrystalline-diamond bodymay be displaced into a porous mass. The silicon and thepre-sintered-polycrystalline-diamond body are reacted to form siliconcarbide within the at least a portion of the interstitial regions.

There is a need to provide a polycrystalline diamond (PCD) elementhaving enhanced thermal stability. There is also a need to provide a PCDelement having enhanced thermal stability combined with enhancedresistance to fracture.

SUMMARY

A purpose of the invention is to provide a polycrystalline diamond (PCD)element having enhanced thermal stability, and a further purpose of theinvention is to provide a method for making same.

A first aspect of the invention provides a polycrystalline diamond (PCD)element having internal diamond surfaces, the internal diamond surfacesdefining interstices between them; the PCD element comprising a maskedor passivated region and an unmasked or unpassivated region, theunmasked or unpassivated region defining a boundary with another regionor body, and extending a depth of between about 5 microns and about 600microns from the boundary, in which at least some of the internaldiamond surfaces of the masked or passivated region contact a mask orpassivation medium, and wherein some or all of the interstices of themasked or passivated region and of the unmasked or unpassivated regionare at least partially filled with an infiltrant material.

In one embodiment, the PCD element is bonded to a substrate at aninterface and the unpassivated or unmasked region is adjacent theinterface. In some embodiments, the boundary defined by the unmasked orunpassivated region is the interface between the PCD element and thesubstrate, the unmasked or unpassivated region extending a depth fromthe interface, the depth being at most about 400 microns, at most about200 microns, at most about 100 microns, at most about 50 microns, atmost about 10 microns or even at most about 5 microns. In someembodiments, the unmasked or unpassivated region extends a depth intothe PCD element from the interface between the PCD element and thesubstrate, the depth being at least about 5 microns, at least about 10microns, at least about 50 microns, at least about 100 microns, or evenat least about 200 microns.

In one embodiment, at least some of the internal diamond surfaces of themasked or passivated region are coated with a mask or passivationmedium.

In one embodiment, some or all of the interstices of the masked orpassivated region and of the unmasked or unpassivated region are atleast partially filled with an infiltrant material having substantiallythe same composition.

In one embodiment, the thermally stable region is proximate a peripheralsurface of the PCD element. In one embodiment, the PCD element has aperipheral surface and a generally annular region adjacent theperipheral surface, at least part of the annular region being thermallystable and being masked or passivated.

In one embodiment, the infiltrant material comprises a catalyst materialfor diamond, and in one embodiment, the catalyst material comprisescobalt, iron or nickel, or an alloy including any of these elements. Inone embodiment, the infiltrant comprises a material that is not acatalyst material for diamond, and in some embodiments the infiltrantmaterial comprises silicon or aluminium.

In some embodiments, the mask or passivation medium comprises an inertsalt, ceramic precursor material, organometallic precursor material orcarbonaceous material. In some embodiments, the mask or passivationmedium is a ceramic material selected from silicon carbide, titaniumcarbide, tantalum carbide, tungsten carbide, hafnium carbide, molybdenumcarbide, zirconium carbide, vanadium carbide and aluminium carbide. Inone embodiment, the mask or passivation medium, or at least a portionthereof, is formed by reaction of a mask or passivation precursormaterial and diamond from the internal diamond surfaces. In someembodiments, the mask or passivation precursor material comprisessilicon, titanium, tantalum, tungsten, hafnium, molybdenum, zirconium,vanadium or aluminium. In some embodiments, remnants of the mask orpassivation precursor material remain within interstices of the PCDelement and may also function as mask or passivation media.

In some embodiments, the interstices within the masked or passivatedregion are least about 50 percent, at least about 70 percent, at leastabout 80 percent or even at least about 90 percent filled with siliconcarbide or aluminium carbide.

In one embodiment, at least 40 percent of the total surface area of theinternal diamond surfaces of the masked or passivated region is coatedwith the mask or passivation medium.

In one embodiment, the masked or passivated region is located adjacent aworking surface or peripheral surface, or both, of the PCD element.

In some embodiments, the masked or passivated region extends a depthinto the PCD element from a working surface, the depth being at mostabout 1,000 microns, at most about 500 microns or at most about 100microns. In some embodiments, the masked or passivated region extends adepth into the PCD element from a working surface, the depth being atleast about 5 microns, at least about 10 microns, at least about 50microns, at least about 100 microns, or even at least about 200 microns.

In one embodiment, the thermally stable region is in the form of astratum or layer. In some embodiments, the masked or passivated regionis in the form of a layer or stratum that extends to a depth of at leastabout 40 microns, at least about 100 microns or even at least about 200microns from a working surface.

Embodiments of the invention may have the advantage of enhanced thermalstability combined with enhanced resistance to fracture, which mayresult from reduced residual stresses.

In one embodiment, the infiltrant material is dispersed through at leastsome of the masked or passivated region and is chemically substantiallyisolated from and substantially unable to interact chemically with thePCD by the coated mask or passivation medium.

In one embodiment, the masked or passivated region and the thermallystable region overlap each other. In one embodiment, the masked orpassivated region is contiguous with the thermally stable region of thePCD element.

In one embodiment, the PCD element comprises a thermally stable regionthat is separated from a region of the PCD element containing a catalystmaterial by a barrier, the barrier comprising a mask or passivationmedium.

In one embodiment, the barrier is in the form of a stratum or layer.

In one embodiment, the PCD element is joined to a substrate and theregion containing a catalyst material is adjacent the substrate.

In one embodiment, the porous region extends throughout the PCD element.

Embodiments of the invention have the advantage of enhanced thermalstability. Embodiments of the invention have the advantage of enhancedthermal stability and reduced internal stress, both of which alone or incombination may extend the working life of the PCD compact.

A second aspect of the invention provides a method for manufacturing aPCD element; the method including providing a PCD body having internaldiamond surfaces, the internal diamond surfaces defining interstices,the PCD body containing a thermally stable region and a porous region,in which at least some of the interstices contain at least partlyunfilled pores; introducing a mask or passivation medium proximate orinto the thermally stable region; and introducing at least oneinfiltrant material into the porous region, the mask or passivationmedium at least partly isolating diamond of the thermally stable regionfrom chemical interaction with the at least one infiltrant material.

In one embodiment of the invention, a controlled temperature cycle isemployed in such a manner as to allow sufficient or a certain amount ofthe mask or passivation medium or its precursor to be introducedproximate or into the thermally stable region prior to the at least oneinfiltrant material melting and infiltrating into the porous PCD body.

In one embodiment, the thermally stable region is at least partlyporous, and in one embodiment, the porous region and the thermallystable region wholly or partially overlap, occupying a common volumewithin the PCD body. In one embodiment, the thermally stable region isat least partly porous and the method includes introducing the mask orpassivation medium by filling part or the majority of the pores with themask or passivation medium.

In one embodiment, the method includes introducing mask or passivationmaterial into part or the majority of a porous region disposed adjacenta thermally stable region, the mask or passivation material functioningas a barrier to infiltrant material, and then introducing an infiltrantmaterial into the PCD body; the mask or passivation materials preventingthe infiltrant material from interacting with the thermally stableregion.

In one embodiment, the method includes coating some or substantially allof the internal diamond surfaces of the thermally stable region, atleast partially, with a mask or passivation medium such as an inertmaterial in order to mask or passivate the thermally stable region, inwhole or in part.

In one embodiment, the method includes substantially chemicallyisolating diamond from chemical interaction with the infiltrantmaterial.

In one embodiment, the method includes introducing the infiltrantmaterial into the polycrystalline diamond body simultaneously withintroducing the mask or passivation medium proximate or into thethermally stable region. In one embodiment, the method includesintroducing the mask or passivation medium proximate or into thethermally stable region and then introducing the infiltrant materialinto the polycrystalline diamond body. In one embodiment, the infiltrantmaterial is introduced into a volume of the PCD body, the volume beingat least 10 percent of the total volume of the PCD body.

In one embodiment, the polycrystalline diamond body is integrally bondedto a substrate, which may comprise a cemented carbide material, duringthe same step in which infiltrant material is introduced, and in oneembodiment, the substrate provides the source of the infiltrantmaterial, which may comprise cobalt.

In one embodiment, the PCD body is joined at an interface to a substratecomprising cemented tungsten carbide, and in one embodiment, theinfiltrant material is introduced into a volume of the PCD body that isproximate a surface of the PCD body, the surface being remote from oropposing the interface, the volume having a depth from the surface of atleast about 0.1 mm.

In one embodiment, the method includes removing catalyst material frominterstices of a PCD body. In one embodiment, the thermally stableregion is devoid or substantially devoid of catalyst material.

In one embodiment, the infiltrant material is a catalyst material. Morepreferably the infiltrant material comprises cobalt, iron or nickel, oran alloy including any of these elements.

In one embodiment, the method includes removing catalyst material fromsubstantially the entire volume of the PCD body, thereby providing athermally stable PCD body that is porous throughout.

Embodiments of the method of the invention have the advantage ofpermitting a PCD body to be infiltrated with a catalyst material withoutsubstantially reducing the thermal stability of the thermally stableregion.

In an embodiment of the method in which the PCD body is joined to asubstrate during the infiltration step, catalyst material such as cobaltwithin the substrate may infiltrate into pores within the PCD body,which may promote the formation of a strong bond between the PCD bodyand substrate.

Embodiments of the method of the invention have the advantage ofproducing PCD compacts having both enhanced thermal stability andreduced internal stress, which may extend the working life of the PCDcompact. The infiltration of catalyst material to a depth within the PCDbody may reduce the internal stress that may be generated when twobodies having very different thermo-mechanical properties are bondedtogether. Mere surface-to-surface bonding of a thermally stable diamondbody to a cemented carbide substrate may result in significantthermo-mechanical stresses proximate the interface between them, whichmay lead to failure of the compacts both during manufacturing and inuse, making such compacts uneconomical.

Embodiments of the method that include coating the internal diamondsurfaces of the PCD body in the masked or passivated region have theadvantage that a generally porous microstructure may be retained. Thismay allow for infiltration of infiltrant material into the porousmicrostructure whilst keeping catalyst material isolated from thethermally stable region. This may preserve the thermal stability of atleast part of the PCD body.

Embodiments of the method of the invention have the advantage that thenature and type of carbide substrate used in the final product may bedifferent from that used in the manufacture of the starting PCD body.This may permit the use of a substrate most suitable for sintering thestarting PCD body, and then the use of a different substrate that may bemore suitable for the finished product. In other words, the substrate ofembodiments of the final product is not limited to that used forsintering the PCD body and may be selected to have better properties foruse in a given application.

A third aspect of the invention provides a PCD insert for a tool, theinsert comprising an embodiment of a PCD element according to theinvention.

A fourth aspect of the invention provides a tool comprising anembodiment of an insert according to an aspect of the invention.

In some embodiments, the tool is for machining, drilling, boring,cutting or otherwise forming or degrading a hard or abrasive workpieceor other body, such as rock, concrete, asphalt, metal or hard compositematerials. In some embodiments, the tool is a drill bit for use in earthboring, rock drilling or rock degradation, as may be used in the oil andgas drilling and mining industries. In one embodiment, the tool is arotary drag bit for use in earth-boring and rock drilling in the oil andgas industry.

A fifth aspect of the invention provides a rotary drill bit containing aplurality of PCD inserts, each comprising a respective embodiment of aPCD element according to the invention.

DRAWING CAPTIONS

Non-limiting embodiments of the invention will now be described in moredetail, by way of example only, with reference to the accompanyingdrawings, of which:

FIG. 1 shows a schematic longitudinal cross sectional view of anembodiment of a PCD element.

FIG. 2 shows a schematic expanded cross sectional view of a region ofthe embodiment shown in FIG. 1.

FIG. 3 to FIG. 6 show schematic longitudinal cross sectional views ofembodiments of PCD elements.

FIG. 7A shows schematic perspective views of components used in anembodiment of a method for manufacturing PCD compacts or inserts.

FIG. 7B shows a schematic perspective view of a PCD compact or insert.

FIG. 8 shows a perspective view of a rotary drill bit for boring intothe earth.

The same references in all drawings refer to the same features, unlessotherwise indicated.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, a “mask” is a physical barrier that is capable ofretarding or preventing diffusion or chemical reactions across it.

As used herein, “mask medium” or “mask material” is a medium or materialthat is suitable for forming a mask or functioning as a mask.

As used herein, a “passivation medium” is a medium that is capable ofretarding or preventing certain chemical reactions or phasetransformations, such as the transformation of diamond to graphite.

As used herein, the term “unpassivated or unmasked” in relation to aregion of a PCD body means that the region is substantially free of themask or passivation medium substantially present within a masked orpassivated region of the polycrystalline diamond body.

As used herein, the term “interstices” is understood to mean“interstices or interstitial regions”. Interstices may be filled orunfilled, or partly filled with a binder or filler material.

With reference to FIG. 1 and FIG. 2, an embodiment of a PCD insert 200comprises an embodiment of a PCD element 100 joined to a cementedcarbide substrate 220 at an interface 116. The embodiment of the PCDelement 100 has internal diamond surfaces 102, the internal diamondsurfaces 102 defining interstices 104 between them. The PCD element 100comprises a masked or passivated region 111 and an unmasked orunpassivated region 112, the unmasked or unpassivated region 112defining a boundary 116 with the substrate 220, the boundary being theinterface (both indicated by reference 116), and extending a depth ofbetween about 5 microns and about 600 microns from the boundary 116, inwhich at least some of the internal diamond surfaces 102 b of the maskedor passivated region 111 contact a mask or passivation medium, andwherein some or all of the interstices 104 b of the masked or passivatedregion 111 and of the unmasked or unpassivated region 112 are at leastpartially filled with an infiltrant material.

With reference to FIG. 3 to FIG. 6, embodiments of PCD elements 100 arejoined to cemented carbide substrates 220 to form embodiments of PCDinserts 200 having respective working surfaces 114. The PCD elements 100each have a respective masked or passivated region 111, wherein themicroscopic interstices (not shown) are substantially filled with a maskor passivation medium, and an unmasked or unpassivated region 112,proximate the substrate 220. The embodiments shown in FIG. 3, FIG. 4 andFIG. 5 each comprise a respective further region 113, in which both themask or passivation medium, or precursor thereof, and the catalystmaterial are present.

In the embodiment shown in FIG. 3, the volume of the masked orpassivated region 111 is substantially greater than that of the unmaskedor unpassivated region 112.

In the embodiment shown in FIG. 4, the volume of the masked orpassivated region 111 is substantially smaller than that of the unmaskedor unpassivated region 112.

In the embodiment shown in FIG. 5, the PCD element 100 is bonded to thesubstrate 220 via an intermediate layer 225. The intermediate layer 225comprises diamond grains, metal carbide and a metal.

In the embodiment shown in FIG. 6, the PCD element 100 comprises aporous region 115 proximate the working surface 114. The microscopicinterstices (not shown) within the porous region 115 are substantiallydevoid of mask or passivation medium and of catalyst material. Themasked or passivated region 111 is located intermediate the porousregion 115 and the unmasked or unpassivated region 112.

Embodiments of PCD elements or inserts of the invention may haveparticular application as cutter elements for drill bits, in whichapplications the enhanced thermal stability may extend the working lifeof the tool.

As used herein, a catalyst material for diamond is a material that iscapable of promoting the precipitation, growth and/or sintering-togetherof grains of diamond under a condition of pressure and temperature atwhich diamond is more thermodynamically stable than graphite. Examplesof catalyst materials for diamond are iron, nickel, cobalt, manganeseand certain alloys including any of these elements. Some catalystmaterials for diamond are capable of promoting the conversion of diamondinto graphite at ambient pressure, particularly at elevatedtemperatures.

As used herein, “thermally stable” when used in relation to a PCD bodyor element or region therein is understood to mean that the PCD withinthat region has enhanced resistance to degradation at elevatedtemperatures, particularly temperatures in the range from about 400degrees centigrade to about 800 degrees centigrade. In some embodiments,this may be achieved if less than about 10% of the area of the internaldiamond surfaces of the body or portion thereof is in contact with acatalyst material that is capable of promoting the conversion of diamondinto graphite at ambient pressure.

In one embodiment, the thermally stable region is adjacent a workingsurface or periphery, or adjacent a working surface and periphery of thePCD element.

With reference to FIG. 7A, an embodiment of a method for making a PCDelement includes providing a PCD insert 300 that has been manufacturedusing an ultra-high pressure and high temperature (HPHT) methodwell-known in the art. The insert 300 comprises a PCD element 310integrally bonded to a cemented carbide hard-metal substrate 320. Themicroscopic interstices (not shown) of the PCD element 310 aresubstantially filled with cobalt catalyst material. At least a part ofPCD element 310 is detached from the insert 300 to produce a PCD body311. One way of detaching the PCD element 310 is to grind away thesubstrate 320. The PCD body 311 is treated to remove catalyst materialfrom the interstices to produce a porous and thermally stable PCDelement 312. The porous PCD element 312 is then contacted on one sidewith a second cemented carbide substrate 340 and on the opposite sidewith a source 330 of mask or passivation medium, or a precursor for amask or passivation medium. The source 330 may be in the form of a thinfoil or disc, or powder. The substrate 340 includes tungsten carbidegrains and a cobalt metal binder, the metal binder being capable ofacting as a catalyst material to promote the growth and sintering ofdiamond grains. The porous PCD element 312, thus “sandwiched” betweenthe substrate 340 and the foil or disc 330 is treated at an ultra-highpressure in excess of about 5 GPa at temperatures sufficiently high tomelt the mask or passivation medium or its precursor and to melt thecobalt metal binder of the substrate 340, resulting in some of itinfiltrating as an infiltrant material into the porous PCD element 312.The temperature cycle may be controlled in such a manner as to allowsufficient or a certain amount of the mask or passivation medium or itsprecursor to be introduced into the porous PCD element 312 prior to thecobalt metal binder material melting and infiltrating into the porousPCD element 312. After this treatment, the resulting insert is removedand processed to final dimensions and tolerances to produce anembodiment of a finished PCD insert 200 shown in FIG. 7B, comprising aPCD element 100 joined to a cemented carbide substrate 220.

One embodiment of the method of the invention includes contacting thePCD body with a source of mask or passivation medium, or of a mask orpassivation precursor material, and with a source of infiltrantmaterial. In one embodiment, the PCD body has a thickness between a pairof opposite surfaces of at least about 1.5 mm or at least about 1.8 mm,one of the pair contacted with a source of mask or passivation medium,or of a mask or passivation precursor material, and the other of thepair contacted with a source of infiltrant material.

One embodiment of the method of the invention includes heating a sourceof mask or passivation medium, or of a mask or passivation precursormaterial, to a temperature within the range between the melting point ofthe mask or passivation medium, or the mask or passivation precursormaterial, and the melting point of the infiltrant material, maintainingthe temperature within this range for a period of time sufficient forthe introduction of the mask or passivation medium, or the mask orpassivation precursor material, to be completed. In one embodiment, thetemperature is then increased to greater than the melting point of theinfiltrant material for a period of time for the introduction of theinfiltrant material to be completed.

One embodiment of the method includes contacting one surface of a porousPCD body with a source of silicon, contacting another surface of the PCDbody with a source of cobalt to form an assembly, subjecting theassembly to a pressure of at least about 5.5 GPa, heating the assemblyto a temperature in the range above the melting point of silicon at thepressure and below the melting point of cobalt at the pressure,maintaining temperature within this range for a period of time of atleast about 2 minutes or at least about 3 minutes, and then increasingthe temperature to above the melting point of cobalt at the pressure.

One embodiment of the method includes contacting one surface of a porousPCD body with a source of aluminium, contacting another surface of thePCD body with a source of cobalt to form an assembly, subjecting theassembly to a pressure of at least about 5.5 GPa, heating the assemblyto a temperature in the range above the melting point of aluminium atthe pressure and below the melting point of cobalt at the pressure,maintaining temperature within this range for a period of time of atleast about 1 minute or at least about 2 minutes, and then increasingthe temperature to above the melting point of cobalt at the pressure.

In some embodiments, the period of time is at most about 15 minutes oreven at most about 10 minutes.

The sintered PCD body can be produced in an ultra-high pressure furnaceby sintering together diamond grains in the presence of a catalystmaterial for diamond at a pressure of at least about 5.5 GPa and atemperature of at least about 1,300 degrees centigrade. The catalystmaterial may comprise a conventional transition metal type diamondcatalyst material, such as cobalt, iron or nickel, or certain alloysthereof. The sintered PCD body, as a whole or at least a region thereof,may then be rendered thermally stable, for example, through the removalof the majority of binder catalyst material from the PCD body or desiredregion using acid leaching or another similar process known in the art.

The catalyst material present in the PCD body 311 may be removed by anyof various methods known in the art, such as electrolytic etching,evaporation techniques, acid leaching (for example by immersion in aliquor containing hydrofluoric acid, nitric acid or mixtures thereof) orby means of chlorine gas, as disclosed in international patentpublication number WO2007/042920, or by another method (e.g. asdisclosed in South African patent number 2006/00378).

In one embodiment of the method, two porous PCD bodies, similar to theporous element 312 in FIG. 7A are provided. One of the porous PCD bodiesis infiltrated or permeated with a precursor for a mask or passivationmedium. Preferably, the precursor is a metal that, when in the molten orgas phase, readily reacts with carbon to form a carbide. The precursormay be introduced into the pores of the porous PCD body by contacting abody of the precursor material with the PCD element and heating in avacuum or inert atmosphere to a temperature above the melting point ofthe precursor, and allowing the molten precursor to infiltrate into theporous PCD body. If the precursor is a good carbide former (e.g. Si orTi), then it may react with carbon from the diamond to form a carbidemask or passivation medium. The resulting masked or passivated PCD bodyis then placed in contact with the other porous PCD body, which in turnis placed in contact with a hard-metal substrate containing a source ofcatalyst material such as cobalt. The porous PCD body, thus “sandwiched”between the hard-metal substrate and the masked or passivated PCDelement, is treated at an ultra-high pressure in excess of about 5 GPaat a temperature sufficiently high to melt the metal binder of thesubstrate, resulting in some of it infiltrating into the porous PCDelement. After this treatment, the resulting insert is removed andprocessed to final dimensions and tolerances to produce a finished PCDinsert.

In one embodiment of the method, a PCD insert similar to PCD insert 300in FIG. 7A, is provided. A region proximate the working surface of thePCD element is depleted substantially of catalyst material by means of amethod known in the art, resulting in the region being porous. A mask orpassivation medium, or precursor for a mask or passivation medium, isintroduced into the pores of the porous region to form a coating on theinternal diamond surfaces. For example, the medium or its precursor maybe introduced in vapour form in order to coat as much as possible of thediamond surface area, even substantially all of the diamond surfacearea, with a thin protective coating of the mask or passivation medium.The parameters of the method of introduction may be controlled to retainporosity within the region, the average pore volume having been reducedby the volume of the deposited mask or passivation medium coat. Acatalyst material is then infiltrated into the remaining pores of themasked or passivated region. This may be done by contacting a source ofcatalyst material with the working surface of the PCD element,assembling the PCD insert and the source into a capsule of a kind usedfor HPHT sintering of PCD, and subjecting the assembly to an ultra-highpressure and temperature at which the catalyst material is molten andthe diamond is thermodynamically more stable than graphite. In someembodiment, the pressure is at least about 5.5 GPa, at least about 6 GPaor at least about 6.5 GPa. In one embodiment, the pressure is about 6.8GPa.

The introduction of a mask or passivation medium or a precursor thereofmay be complete, in that the majority of the open porosity of the maskedor passivated region of the PCD body is filled or rendered largelynon-porous by the introduction of a further phase or phases, henceblocking infiltration; or it may be partial, in that only the exposedsurfaces of the diamond microstructure are masked or passivated, withsignificant volume-based porosity remaining, but resulting in anintergrown diamond skeleton or microstructure that is largely isolatedfrom chemical and physical interaction with the infiltrant or bondingmaterial front.

The mask or passivation medium may be removable, for example by somesuitable chemical treatment before use in the final compact, or if inertor even beneficial can be left within the product.

Various methods of introducing mask or passivation media or theirprecursors may be used. These include using a gas phase of, forinstance, Ti, Si, W and the like, to coat the PCD material in the regionor regions thereof that are required to be free of infiltrant material.Alternatively, pores or voids of the structure can be filled, eitherwholly or partially, with an inert salt or ceramic phase. Suitable saltsor ceramics may be those which do not melt at HPHT conditions, orundergo significant phase changes that could compromise the structuralintegrity of the PCD skeleton. A further approach involving treatment ofthe internal surfaces of the porosity using a surface chemistrymodification such that chemical wetting by the infiltrant front isprevented or hindered, is also anticipated.

Non-limiting examples of technologies for introducing mask orpassivation media into the porosity of the diamond skeleton include:

-   -   Atomic Layer Deposition (ALD) to coat the internal diamond        surfaces of the open porosity;    -   infiltration with a liquid pre-ceramic polymer or polymer        solution that is subsequently converted to a ceramic phase        through a process of curing and subsequent ceramitisation;    -   use of sol gel routes or other solution-based chemical routes to        deposit or form suitable phases in the porosity of the PCD,        which may require subsequent heat and/or gas treatments to        achieve the desired phases.

Atomic Layer Deposition (ALD) may form extremely homogeneous coatings onsurfaces which, as a result, are very good barrier layers, even for onlya few (for example 25) atomic layers. In addition, the chemistry can becontrolled layer by layer, allowing multifunctional coatings to beeasily applied. ALD may have advantages over other thin film depositiontechniques because ALD grown films are substantially conformal with thecoated body, pin-hole free and chemically bonded to the coated body.With ALD it is possible to deposit coatings uniform in thickness insidedeep trenches, porous media and around particles. Such an ALD coatingmethod is disclosed, for example, in United States patent publicationnumber 2008/0073127.

A further example alternative approach to introducing a mask orpassivation medium into a porous region within a PCD element is toinfiltrate a preceramic polymer, or other suitable organometallicprecursor material, into the pores (see, for example, U.S. Pat. Nos.5,649,984 and 5,690,706, and the references cited therein, forbackground information). Liquid pre-ceramic polymers exist that can beconverted to ceramics through a process of curing and subsequentcerametisation. In particular, certain Si—C—N liquid preceramic polymersystems may be most suitable for infiltration into porous PCD bodies andsubsequent treatment, as is known in the art, to convert the polymerinto a ceramic material, particularly silicon carbo-nitride, as is alsowell known in the art. Infiltration of a preceramic polymer into porousPCD is advantageously carried out in vacuum and assisted by theapplication of an elevated temperature and/or pressure of less thanabout 30 MPa.

Another method for introducing mask or passivation material into aporous region within a PCD element includes a sol gel method (see, forexample, the approach for depositing metal carbide onto diamonddisclosed in WO2006/032982, and coating methods as described inWO2006/032984 and WO2007/088461). In a particular embodiment, an inertsalt such as CaCo₃, for example, is infiltrated into the porous PCDelement by means of a sol gel approach. The inert salt functions tolimit the subsequent infiltration of catalyst material at an ultra-highpressure and temperature, resulting in a region of the PCD wherein thepores are substantially filled with the salt and a second region whereinthe pores are substantially filled with a catalyst material. The saltmay readily be removed from the PCD element after the reinfiltrationstep by means of dissolution in water, leaving a porous region withinthe PCD.

Other methods may be used to introduce a mask or passivation medium intoa porous PCD body. In an example embodiment of one such alternativeapproach, a porous PCD element may be infiltrated or permeated with avapour of tungsten hexafluoride, resulting in the deposition of tungstenwithin the pores. At least some of the tungsten may react with carbonfrom the diamond to form WC, which is a suitable passivation medium.Since unreacted tungsten is also a suitable mask or passivation medium,the formation of WC would not be essential. Methods known in the art ofdiamond coatings and metallization may be used (see, for example, U.S.Pat. Nos. 7,022,403; 5,346,719; 5,062,865; and 5,062,865). Vapourdeposition approaches may similarly be used for introducing Si, Cr or Tiinto the interstices of a porous PCD element, resulting in a carbide,nitride, boride, carbo-nitride or boro-nitride of silicon, chromium ortitanium at least partially coating the diamond surfaces. Such methodsare well known in the art of diamond coating by means of physical vapourdeposition (PVD) and chemical vapour deposition (CVD). See, for example,WO2005/078041, U.S. Pat. Nos. 5,024,680 and 5,221,969, and Europeanpatent number EP 0 467 404, which are incorporated herein by reference.

In one example embodiment, the porosity may be filled wholly or partlywith a non-diamond carbon containing material. This may, in the presenceof catalyst material be converted to PCD during a subsequent step ofsubjecting the PCD body to an ultra high pressure, resulting inincreased diamond density in the outer portion of the PCD layer andhence increased thermal stability. Infiltration with a carbon-containingmaterial may be accomplished by chemical vapour infiltration ofamorphous graphitic carbon supplied at low pressure using gaseoushydrocarbons including methane, ethane or ethylene. Infiltration mayalso be achieved by liquid phase infiltration at high pressure usingliquid hydrocarbons, including wax, pitch and bitumen or by impregnationwith carbon at high pressure using fullerenes.

In a further example embodiment, an intermediate layer may be provided,for example between the substrate and the PCD body. The function of theintermediate layer may be primarily to reduce internal stresses withinthe PCD element and therefore minimise the risk of fracture. Suchintermediate layers are well known in the art and various intermediatelayers for PCD inserts have been disclosed (e.g. U.S. Pat. No. 5,370,195and US patent publication number US 2007-0186483 A1).

The mask or passivation process may be conducted in such a manner as toleave or render porous a region adjacent the substrate or supportsurface to ensure optimal bonding during the HPHT bonding step.

The masked or passivated region may be formed between the thermallystable region and the porous region adjacent the substrate or supportregion, provided it acts as a barrier to any bonding phase infiltratingfrom the substrate or support, preventing it from contacting orinteracting in any way with the thermally stable region.

A region adjacent a peripheral surface of the PCD element may be treatedto form a thermally stable annular region substantially free of catalystmaterial. In an alternative example embodiment, the passivated or maskedregion could be located intermediate the thermally stable region,adjacent the working surface and/or periphery, and the porous regionadjacent the surface to be attached to the substrate. The variousregions are typically provided in layer form.

Preferably, the mask or passivation step will not be carried out underHPHT conditions, and will therefore constitute a separate treatment ofthe porous PCD body under moderate temperature and pressure conditionsbefore it is bonded to the substrate or support body.

In one example embodiment of the method of the invention, the attachmentor bonding of a previously sintered or intergrown thermally stable PCDbody having substantial diamond-to-diamond bonding in its microstructureto a suitable support, such as a cemented carbide substrate, is providedin such a way as to maintain or preserve the thermal stability of thePCD, particularly at the upper working surface of the resultant abrasiveelement. Hence the need for any subsequent treatment or modification ofthe PCD body in order to improve or attain final thermal stability ofthe region adjacent the working surface or periphery may be removed orsignificantly reduced. In use, PCD elements may be exposed to elevatedtemperatures due to friction events at the working or outer surface.Hence, it is typically in this region that thermal stability must bepreserved.

The provision of a degree of porosity in the PCD body may assist infacilitating the bonding of the PCD body to the substrate. Porosity in aregion of the PCD that will contact the substrate may allow betterbonding between the substrate and the PCD body because of infiltrationof the cementing phase or another suitable bonding phase from thesubstrate body or the interface region into the PCD body. While wishingnot to be bound by a particular hypothesis, the porosity may facilitatea capillary action which may draw the bonding phase into the PCDmicrostructure and maximise the strength of the bond between the twobodies during the attachment process.

The person skilled in the art will appreciate that PCD elements andinserts of a wide range of shapes and sizes can be made, depending onthe type of application. The inserts may be particularly advantageouswhen used in applications where the insert may be subjected to hightemperatures, and therefore where high thermal stability is important.One such use is for rotary drill bits used for rock drilling and earthboring in the oil and gas industry.

With reference to FIG. 8, an embodiment of an earth-boring rotary drillbit 800 includes, for example, a plurality of PCD inserts 600 aspreviously described herein with reference to FIG. 1. The earth-boringrotary drill bit 800 includes a bit body 802 that is secured to a shank804 having a threaded connection portion 806 (e.g., a threadedconnection portion 806 conforming to industry standards such as thosepromulgated by the American Petroleum Institute (API)) for attaching thedrill bit 800 to a drill string (not shown). The bit body 802 maycomprise a particle-matrix composite material or a metal alloy such assteel. The bit body 802 may be secured to the shank 804 by one or moreof a threaded connection, a weld, and a braze alloy at the interfacebetween them. In some embodiments, the bit body 802 may be secured tothe shank, 804, indirectly by way of a metal blank or extension betweenthem, as known in the art.

The bit body 802 may include internal fluid passageways (not shown) thatextend between the face 803 of the bit body 802 and a longitudinal bore(not shown), which extends through the shank 804, an extension 808 andpartially through the bit body 802. Nozzle inserts 824 also may beprovided at the face 803 of the bit body 802 within the internal fluidpassageways. The bit body 802 may further include a plurality of blades816 that are separated by junk slots 818. In some embodiments, the bitbody 802 may include gage wear plugs 822 and wear knots 828. A pluralityof PCD inserts, which are generally indicated by reference numeral 600in FIG. 8, may be mounted on the face 803 of the bit body 802 in cuttingelement pockets 812 that are located along each of the blades 816.

The inserts 600 are positioned to cut a subterranean formation beingdrilled while the drill bit, 800, is rotated under weight on bit (WOB)in a bore hole about centreline, L800.

Embodiments of PDC inserts of the present invention may also be used asgauge trimmers, and may be used on other types of earth-boring tools.For example, embodiments of inserts of the present invention may also beused on cones of roller cone drill bits, on reamers, mills, bi-centrebits, eccentric bits, coring bits, and so-called hybrid bits thatinclude both fixed cutters and rolling cutters.

EXAMPLES

The invention will now be described, by way of example only, withreference to the following non-limiting examples.

Example 1

A PCD insert suitable for use on a rotary bit for oil and gas drillingand having a diameter of about 16 mm was provided. The insert wassubstantially cylindrical in shape and comprised a PCD layer integrallybonded to a Co-cemented WC substrate. The PCD layer was about 2.3 mmthick and comprised sintered diamond grains with an average grain sizeof less than about 20 microns and with a grain size distribution whichwas capable of being resolved into at least three distinct peaks, ormodes. The interstices between the diamond grains of the PCD were filledwith Co, a catalyst material sourced from the hard-metal substrateduring the step of sintering the PCD. The PCD layer was detached fromthe substrate by means of wire EDM (electro-discharge machining),providing a PCD body having a generally disc-like shape. Substantiallyall of the Co was then removed from the PCD body by immersing it in amixture of hydrofluoric and nitric acid for several days, resulting in aporous, detached PCD body. The porous PCD body was heat treated invacuum in order to remove (i.e. “outgas”) any residual organicimpurities that may have been present.

The porous PCD body was placed onto a flat surface of anothercylindrical substrate comprising cobalt-cemented tungsten carbide, and athin disc of silicon placed on top of the porous PCD disc, and thisassembly was loaded into a capsule for an ultra-high pressure furnace(or high temperature press). Although a disc of silicon was used in thisexample, a layer of silicon powder could be used. The silicon disc wasless than 1 mm thick and had been ultrasonically cleaned in an acetonebath. The assembly was subjected to an ultra-high pressure of greaterthan about 5.5 GPa, at which diamond is thermodynamically stable. Thetemperature was increased to about 1,220 degrees centigrade, which wasgreater than the melting point of silicon at the pressure, andmaintained between this temperature and about 1,320 degrees centigrade,which is approximately the melting point of cobalt at the pressure, fora period of 3 minutes. This period had been determined byexperimentation to be sufficient for the silicon to melt and infiltrateinto the PCD body to a depth from the substrate of greater than about100 microns and less than about 400 microns. The temperature was thenincreased to about 1,400 degrees centigrade and maintained at this levelfor about 5 minutes. In this way, the porous PCD body was re-infiltratedto a depth of between 100 and 400 microns with molten cobalt from thesubstrate and molten silicon from the opposite surface, andsimultaneously bonded to the substrate.

After the re-infiltration step, the insert was recovered and sliced intotwo parts along an axial plane, producing two cross-sectional surfaces.One of these surfaces was polished and analysed by means of SEM(scanning electron microscopy). It was found that the silicon hadinfiltrated the PCD to a depth of several hundred microns andsubstantially all had reacted with carbon from the diamond to form SIC.The interstices near the side of the PCD bonded to the substrate weresubstantially filled with Co, which had infiltrated from the substrate,and there was a layer between the silicon-rich and the cobalt-richlayers in which the interstices were substantially filled with both Coand Si. Further analysis revealed that cobalt disilicide was presentwithin the intermediate layer.

Example 2

A porous PCD body can be prepared as in Example 1 and silicon can beintroduced into some of the pores prior to the treatment at ultra-highpressure. This can be done by placing the porous PCD disc into agraphite vessel and disposing a silicon foil on top of it, the siliconfoil having been ultra-sonically cleaned in an acetone bath. The vesselcan be placed in a furnace and its contents heated in a vacuum to about1,550° C., causing the silicon foil to melt and infiltrate the PCD disc.When the PCD body is removed from the furnace after re-infiltration, itis anticipated that the interstices will be filled with silicon carbideand a minor amount of unreacted silicon to a depth of about 200 microns.

Such a partially infiltrated PCD body can be placed onto acobalt-cemented tungsten carbide substrate, with the non-infiltratedside (i.e. the side of the PCD on which the interstices aresubstantially empty and the PCD body is porous) in contact with asurface of the substrate. This assembly of PCD disc and substrate canthen be subjected to an ultra-high pressure of greater than about 5.5GPa and a temperature of greater than about 1,500° C. to produce a PCDinsert.

Example 3

A porous PCD body can be prepared as in Example 1 and silicon can beintroduced into some of the pores prior to the treatment at ultra-highpressure. Only a very thin film of silicon can be deposited onto a flatsurface of the PCD disc by means of sputtering. The mass of the silicondeposited should be calculated to be just sufficient for 10% of thepores to be filled with silicon carbide, and consequently to providejust enough silicon to infiltrate the PCD to a depth of about 10% of itsthickness, i.e. to a depth of about 230 microns from the flat surface,leaving the remaining pores substantially empty. This mass, whencalculated, will typically be about 12 milligrams, providing a film ofabout 23 microns thick, the film thickness being as uniform as possibleacross the PCD surface.

The silicon-coated PCD can then be placed into a graphite vessel, withthe coated surface remote from the base of the graphite vessel (i.e. onthe top surface), and the vessel then placed into a furnace. The vesseland its contents are to be heated in a vacuum to 1,550° C., thistemperature being above the melting point of silicon, to produce a PCDinsert.

Example 4

A porous PCD body was prepared as described in Example 1. The porous PCDbody was placed onto a flat surface of a cylindrical substratecomprising cobalt-cemented tungsten carbide, and a layer of aluminiumpowder was introduced on top of the porous PCD disc. The layer ofaluminium powder had a mass of about 135 mg and the mean size of thepowder was in the range of about 5 microns to 20 microns. Althoughaluminium powder was used in this example, an aluminium disc or foilcould also be used. The mass of the aluminium powder was estimated tocorrespond to a fully dense volume of aluminium equivalent to about 10percent of the volume of the PCD body. This assembly was loaded into acapsule for an ultra-high pressure furnace (or high temperature press).The aluminium layer was less than about 1 mm thick. The assembly wassubjected to an ultra-high pressure of greater than about 5.5 GPa, atwhich diamond is thermodynamically stable. The temperature was increasedto about 900 degrees centigrade, which was greater than the meltingpoint of aluminium at the pressure, and maintained between thistemperature and about 1,330 degrees centigrade, which was the meltingpoint of cobalt at the pressure, for a period of 1 minute. This periodhad been determined by experimentation to be sufficient for thealuminium to melt and infiltrate into the PCD body to a depth from thesubstrate of greater than about 100 microns and less than about 400microns. The temperature was then increased to about 1,500 degreescentigrade and maintained at this level for about 5 minutes. In thisway, the porous PCD body was re-infiltrated to a depth of between 100and 400 microns with molten cobalt from the substrate and moltenaluminium from the opposite surface, and simultaneously bonded to thesubstrate.

After the re-infiltration step, the insert was recovered and sliced intotwo parts along an axial plane, producing two cross-sectional surfaces.One of these surfaces was polished and analysed by means of SEM(scanning electron microscopy), revealing that the PCD had bonded wellwith the substrate. Further analysis by means of energy dispersivespectroscopy (EDS) and other techniques revealed that and thatsubstantially all of the interstices within a region of the PCD furtherthan about 150 microns from the interface with the substrate were filledwith aluminium carbide. A minor amount of other aluminium containingcompounds and cobalt was observed throughout this region. The PCDinterstices within about 150 microns from the substrate were filledprincipally with cobalt, although some aluminium was evident.

Further test inserts were made as above and subjected to a wear test,which involved using the inserts, suitably prepared as would beappreciated by the skilled person, to mill a granite block mounted on avertical turret milling apparatus. The PCD layer displayed excellentwear resistance and thermal stability. As a control, a PCD insert wasmade using a PCD body that had not been infiltrated with aluminium. Themeasure of performance in this test was distance of granite cut beforethe onset of “rubbing”, in which the depth of the cut into the granitebegins to decrease, indicating decreased cutting effectiveness. Thisdistance was about 750 mm in the case of the control insert and in therange from about 3,500 mm to about 6,200 mm in the case of the testinsert.

Example 5

A porous PCD disc can be prepared using the process described in Example1 and aluminium can be introduced into the pores prior to the treatmentat ultra-high pressure. This can be done by placing the porous PCD discinto a graphite vessel, and disposing an aluminium foil on top of it,the aluminium foil having been ultra-sonically cleaned in an acetonebath. The vessel can then be placed in a furnace and its contents heatedin a vacuum to above the melting point of aluminium, i.e. to about 900degrees centigrade, causing the aluminium foil to melt and infiltratethe PCD disc.

Example 6

A porous PCD disc can be prepared using the process described in Example1 and aluminium can be introduced into the pores prior to the treatmentat ultra-high pressure by depositing a very thin film of aluminium ontoa flat surface of the PCD disc by means of sputtering. The mass of thealuminium deposited can be calculated to be just sufficient for 10% ofthe pores to be filled with aluminium carbide, and consequently toprovide just enough aluminium to infiltrate the PCD to a depth of about10% of its thickness, i.e. to a depth of about 230 microns from the flatsurface, leaving the remaining pores substantially empty. This masscould be about 14 milligrams, providing a film about 23 microns thick,the film thickness being as uniform as possible across the PCD surface.

The aluminium-coated PCD can be placed into a graphite vessel, with thecoated surface, remote from the base of the graphite vessel (i.e. on thetop surface), and the vessel placed into a furnace. The vessel and itscontents can then be heated in a vacuum to 900 degrees centigrade, thistemperature being above the melting point of aluminium and one at whichaluminium carbide forms readily when in contact with a source of carbon.This would result in the masked PCD body having a stratum of about 230microns thick comprising aluminium carbide in the interstices.

The masked PCD body can then be assembled into a capsule, the end of thePCD body opposite the stratum being in contact with a cobalt cementedcarbide substrate, or other source of cobalt, and subjected to apressure of at least about 5.5 GPa and a temperature of at least about1,350 degrees centigrade. Cobalt would infiltrate from the source intothe porous region of the PCD but not into the stratum containing thealuminium carbide, resulting in a thermally stable PCD element.

The invention claimed is:
 1. A polycrystalline diamond (PCD) elementhaving internal diamond surfaces, the internal diamond surfaces defininginterstices between them; the PCD element comprising a masked orpassivated region and an unmasked or unpassivated region, the masked orpassivated region extending a depth into the PCD element from a workingsurface of at least 100 microns, the unmasked or unpassivated regiondefining a boundary with another region or body, and extending a depthof between 5 microns and 600 microns from the boundary, in which atleast some of the internal diamond surfaces of the masked or passivatedregion contact a mask or passivation medium, and wherein some or all ofthe interstices of the masked or passivated region and of the unmaskedor unpassivated region are at least partially filled with an infiltrantmaterial.
 2. A PCD element as claimed in claim 1, in which at least someof the internal diamond surfaces of the masked or passivated region arecoated with a mask or passivation medium.
 3. A PCD element as claimed inclaim 1, in which some or all of the interstices of the masked orpassivated region and of the unmasked or unpassivated region are atleast partially filled with an infiltrant material having the samecomposition.
 4. A PCD element as claimed in claim 1, in which theinfiltrant material comprises silicon or aluminium.
 5. A PCD element asclaimed in claim 1, in which the infiltrant material comprises acatalyst material for diamond.
 6. A PCD element as claimed in claim 1,in which the mask or passivation medium is a ceramic material selectedfrom silicon carbide, titanium carbide, tantalum carbide, tungstencarbide, hafnium carbide, molybdenum carbide, zirconium carbide,vanadium carbide and aluminium carbide.
 7. A PCD element as claimed inclaim 1, in which the interstices within the masked or passivated regionare at least 50 percent filled with silicon carbide or aluminiumcarbide.
 8. A PCD element as claimed in claim 1, in which at least 40percent of the total surface area of the internal diamond surfaces ofthe masked or passivated region is coated with the mask or passivationmedium.
 9. A PCD element as claimed in claim 1, the PCD element beingbonded to a substrate at an interface, the boundary of the unmasked orunpassivated region being defined by the interface, the unmasked orunpassivated region extending a depth into the PCD element from theinterface, the depth being at most 400 and at least 5 microns.
 10. A PCDelement as claimed in claim 1, in which the masked or passivated regionextends a depth into the PCD element from a working surface, the depthbeing at most 1,000 microns.
 11. A PCD element as claimed in claim 1,the PCD element comprising a thermally stable region, in which themasked or passivated region defines a barrier between the thermallystable region and the unmasked or unpassivated region of the PCDelement.
 12. A PCD insert for a tool, the insert comprising a PCDelement as claimed in claim
 1. 13. A tool comprising a PCD insert asclaimed in claim
 12. 14. A rotary drill bit containing a plurality ofinserts, each insert being as claimed in claim 12.